PROJECT 3 SUMMARY/ABSTRACT Several drugs, including NSAIDSs and methotrexate, used to treat pediatric inflammatory conditions are dependent on renal drug transporters for some of their elimination. Anakinra, also used to treat inflammatory conditions, may alter the renal transporter expression or post-translational processing. In the dynamic setting of the postnatal developing kidney, when expression of the most relevant drug transporters--the organic anion transporters OAT1 and OAT3--is rapidly changing, the effects of these inflammatory therapies on renal drug secretion is likely to be quite complex. These effects will be hard to unravel without gaining a clear understanding of how drug transporter expression relates to apical-basolateral polarization so that optimal vectorial drug transport occurs (e.g., the capacity of the renal proximal tubule to transport drugs (methotrexate) from plasma to urine).. Here, we focus on the renal drug transporters OAT1 (originally discovered by our group) and OAT3, as well as other drug transporters during postnatal and juvenile maturation of the kidney. Specifically, we will address how message and protein levels, subcellular localization, apical-basolateral polarization, and the function of these transporters is regulated during the developmental stages of kidney maturation. A detailed analysis of the spatio-temporal coordination of these processes in relation to renal secretion will also be very helpful for improving pediatric physiologically-based pharmacokinetic model systems. In our studies, functional maturation will be assessed by measurement of transport of labeled substrates. We will employ a combination of in vitro, ex vivo and in vivo animal studies (using wild type and knockouts) and, with an eye to translational studies (in collaboration with other RPDP investigators), human progenitor stem cell (hPSC)-derived renal organoids, which differentiate to the point of substantial expression of OATs and other drug transporters. Focusing on drugs used for inflammatory conditions, we aim to address the following questions: SA1) What is the temporal relationship of OAT1, OAT3 and other drug transporter expression, post-transcriptional processing, and apical-basolateral membrane sorting to the acquisition of drug transport capacity during proximal tubule maturation? SA2) Can renal organoids derived from human iPS cells be used as a model for understanding the regulation of OATs and other drug transporters in the context of renal secretion (as a function of the aforementioned cell biological processes)? We expect to generate a great deal of time series omics, microscopic and functional data. Importantly, we have considerable experience in systems biology and computational data integration--and we have the support of expert collaborators and cores. Consistent with the Pediatric Transporter Working Group Recommendations, these studies will: ?Investigate basic developmental mechanisms regulating transporter expression and activity in the different organs,? and per this RFA, Perform non-clinical...research to understand mechanisms of age- and developmentally- related changes in metabolism and response to medicinal products.